Master clock system



Sept. 22, 1953 J. STERN MASTER CLOCK SYSTEM 4 Sheets-Sheet 1 Filed Nov. 15. 1948 llllullllllllll IN V EN TOR. IBM 15' J 5 TEEN masrew. (Loan I SRONOARY (Lock; I

IIE l Sept. 22, 1953 L, J, ST ERN 2,652,683

MASTER CLOCK SYSTEM Filed Nov. 15. 1948 4 Sheets-Sheet 2 Sept. 22, 1953 L. J. STERN 2,652,633

I MASTER CLOCK SYSTEM Filed Nov. 15. 1948 4 Sheets-Sheet 3 0 van for may J 556222 flzfq Se t, 22, 1953 L. J. SQTERN 2,652,683

MASTER CLOCK SYSTEM Filed Nov. 15. 1948 4 Sheets-Sheet 4 //7 Men for Patented Sept. 22, 1953 MASTER CLOCK SYSTEM Lewis J. Stern, Adrian, Mich., assignor to Sperti Faraday, Inc., Adrian, Mich., a corporation of Ohio Application November 15, 1948, Serial No. 60,135

8 Claims. 1

This invenion relates to master clock systems. More particularly, it deals with a system of a plurality of independent electric clocks which are periodically and automatically corrected or reset at regular intervals by a master clock, such as in a system of clocks for different rooms in a school or a hospital building.

This invention is an improvement of my copending application Serial No. 456,718 filed August 29, 1942, now U. S. Patent 2,498,462 issued February 21, 1950, including modifications for practically adapting the system of this patent for operating a large number of clocks, and modifications in the construction of the secondary clocks subservient to the master clock.

It is an object of this invention to produce a simple, efficient, effective and economic master clock system.

Another object is to produce such a system for automatically resetting a large number of separately driven electric clocks at regular intervals by one master electric clock.

Another object is to improve the driving and clutch mechanisms of the secondary clocks to prevent the motors from stalling and/or winding up' the torsion in the gears of the clocks when they are stopped for resetting by the master clock during the correction interval.

Another object is to provide manual means for resetting simultaneously the master clock and all of the separately driven secondary clocks independently of their automatic correction and reset controlled by the master clock.

Another object is to improve the system of the prior U. S. Patent No. 2,498,462.

Generally speaking, the system of this invention comprises a master electric clock and a plurality of separately driven secondary electric clocks, all of which are driven from a common synchronous alternating current source. The automatic control of the correction of these clocks is provided through two direct current sources of different voltage, one of which voltage sources is controlled to speed-up the clocks to a pre-set stop point and the other of which is to release the stop after all of the clocks have reached this point. All three of these currents are conducted to the secondary clocks from the control means over only three conductors, one of which is common for the return of all of the currents and the other two of which are for the sending of the two difierent direct current voltages, one of which two alternates between one direct voltage and the alternating current source. Thus, the voltage which is employed for releasing the stops may be transmitted over the same circuit asthe regular alternating current for running the secondary clock motors, but since all of the secondary clocks are advanced to await the proper pre-set release point, the interruption of the alternating current does not cause a delay.

The automatic control for resetting the clocks may be provided at regular intervals, such as once each hour, and this interval may be determined by a contact provided in the master clock circuit, which starts the control means. This control means comprises a series of motor actuated cams and corresponding control relays that control the current to operate the speed-up and release and regulate alternating current supplied to the secondary clocks of the system. This control interval preferably has a short duration, such as about one minute, and for example may occur during the 33rd or 34th minute after each hour.

Th mechanisms of the clocks of this system are driven through a plurality of friction clutches, one or the other of which is always engaged either through direct drive or speed-up of the clocks, so that in the event one of the clocks reaches its stop before another, the motor in that clock will not be stalled. Also each clock has an electromagnet actuated by one of the direct current voltages for operating the speed-up device, and each of the secondary clocks has a second electromagnet actuated by the other direct current voltage for operating the release device, which second electromagnet may be connected in series with the induction motor for driving the.

secondary clocks so that said other direct current voltage and the alternating driving current may be alternately conducted through the same circuit in the secondary clocks, thus reducing the number of conductors required for their correction control.

There may be provided a manually controlled circuit for resetting or correcting all of the clocks, which circuit is independent of the automatic control means, but employs the same conductors between the secondary clocks and the current sources.

The above mentioned and other features and objects of this invention and the manner of attaining them are given more specific disclosure in the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

Fig. 1 is a schematic wiring diagram of the system of this invention, disclosing a master clock and a plurality of secondary clocks with their three current supplies, and their automatic and manual correcting and resetting control means;

Fig. 2 is a fragmentary View of the face of one of the master or secondary clock mechanisms showing in dotted lines some of the drive gearing therefor;

Fig. 3 is a partial view taken from the left of Fig. 2 showing part of the gear train from the driving motor shaft, and th clutches employed in this gear train for speeding-up the clock mech anism during reset intervals;

Fig. 4 is a partial sectional side view taken from the right of Fig. 2, showing the gearing between the speed-up clutch mechanism and the time indicators or hands of the: clock;

Fig. 5 is a reduced face view ofa secondary clock with parts of the face broken away, showing the clock stop lever and control device;

Fig. 6 is a section taken along line VI-'VI of Fig. 5 of the stop lever and release magnet therefor;

Fig. 7 is a view of the back of a secondary clock showing the location ofthe electromagnetic coils and their electrical connections in relation to the electric clock motor;

Fig. 8 is a fragmentary front view of the master clock, with a portion of the face broken away, to show the mechanism for governing the automatic reset or correction interval for the secondary clocks of the system.

Before describing the electrical control circuit of Fig. l the mechanism of the mechanical drive of the electric clocks and their speed-up, stop and release devices will be described so that the operation of the circuitof Fig. 1 may be better understood.

I. CLOCK MECHANISMS l. The speed-up device Referring first to Figs. 2, 3 and 4, the gears for operating the clocks may be mounted between a pair of parallel plates or disks I and 2 which are held together by a plurality of posts 3. On the outside of back plates 2, a synchronous motor unit 4 (see Fig. 4) which may have a built-in gear reduction housing 5, may be mounted by means of suitable screws 6. Projecting through the plate 2 from the units 4 and 5 may be a motor drive shaft '4 (see Figs. 2 and 3) which may be driven at a reduced rate by the electric synchrono'us clock motor 4. Fixed on this shaft 1 may bev a pinion 8 in mesh with a gear 9 which is loosely mounted on a shaft I0, between the plates I and 2 parallel with the shaft 7. Also loosely mounted on the shaft I is a second gear 9 which is urged into contact with the gear 9 by means of a spring 9 against a pair of friction disks 91 on each side of said gear 9", so that there is a slip friction engagement between the motor and the remaining of the gear mechanism. In mesh with the friction driven pinion 9 is a larger gear II which also meshes with a loose pinion I2 mounted on a stem or shaft I3 parallel to the shafts l and I0.

Connected to one side of the pinion I2 (Fig. 4) may be a larger diameter crown-toothed clutch disk I4 which together with the pinion I2 is axially movable along the shaft I3. Also connected with the pinion I2 and clutch disk I4 is a tubular extension i connected to an axially movable core of an electromagnet. This tube I5 extends through an aperture in the plate 2 and is surrounded by the coil I6 of the electromagnet, mounted on the plate 2 by means of posts IT. A compression helical spring I8 on the pin or loose shaftI 3 normally urges the tube I5 together with its pinion I2 and clutch I4 towards the face plate I in the position shown in Fig. 3, which is out 01' engagement with the complementary crowntoothed clutch face gear I9 which rotates freely on a hollow stud around tube I5. Spring I8 urges the tube I5, clutch plate I4 and pinion I2, to engage the pinion I2 with a fiber clutch disk- 20, which may be fixed to another pinion gear 2| loosely mounted on the stem I3?, and in mesh with a larger gear 22 (see Fig. 4). The gear 22 has fixed thereto a long pinion 23 in mesh with the normally loose gear I9, as Well as in mesh with the minute hand gear 24, which is connected with the shaftor. sleeve 25 through a bearing in the face plate I; to the minute hand 26 of the clock. Thus, in. the normal operation, the minute handis driven back through its gear 24, long pinion 23, gear 22, pinion 2I, clutch 20, pinion I2, gears II and 8", clutches 9 and gears 9 and 3 to the motor drive shaft 1. The large complementary gear portion I9 of the crowntoothed clutch, which also, is driven by the pinion 23, merely. idles on the core I5 since it is out of mesh with the crown-toothed clutch plate I4, as shown in Fig. 3.

For driving thehour hand of the clock there may be provided a second pinion 21 on the hollow shaft 25 which meshes with a gear28 affixed on a coaxial adjacent pinion gear 29 that drives .the larger gear 38 on a cylindrical shaft 3| surrounds ing the shaft 25, to which-is attachedthe hour hand 32.

When speed-up is required, the coil IGmay be energized with a low voltage direct current. as will be described later, and the core I5. with gear I2 and clutch plate I4 is pulled towards the back plate 2, into the position shown in Fig. 4, so that the crown-toothed clutch members I4-and I9. are in mesh, and the friction clutch 20 is released from the pinion 2!. The drive is now through the large gear I9 to the pinion 24, and piniongear ZI is now an idler. The difference in ratio between the gears 2I and 22 is now reversed. through gears I9 and. 23, and the hands of the mechanism are speeded up materially,-say for example-about 60 times, as the clock motor continues to operate. However, as soon as the direct current iscut-off through the coil I6, the spring I8 disengageszthe clutch I4 and reengages the'clutch-2Il, sothat normal operation will resume as previously described.

The above described mechanismofFigs. 2, 3 and 4 may be thesame, and preferablyis the same, for all of the secondary clocks as well as the master clock, although the clutch 9" isnot required in the master clock.

2. Secondary clock stop and release devices Referring now to Figs. 4, 5, 6 and '7, there is shown on the minute hand gear 24 of each clock, an axially parallel extending peg 33, projecting towards the rear face plate 2. InFigs. 5 and 6 there is shown a bracket base 34 having upstanding lever guides 35 and 36, in the former of which may be provided a headed pin or a pivot 31 which extends through a slot 38 in one end of a slidable bar or stop lever 39', which lever 33 may both slide and pivot on the pin 31. Extending perpendicularly from one side of the lever .39 may be anarm 49 which projects into the normal path of the rotating peg 33 (see Fig. 5), so that asthe minute hand wheel 34 turns in the direction of the arrow, the peg 33 will hit against the arm 40, and pull or slide the lever 39 longitudinally in its pivot31 the length of the slot 38, against the actionbf a.

helical tension spring 4| connected between the lever 39 and the fixed lever guide 36 (see Fig. 6). Near the other end of the lever 39, there may be provided a leg 42 projecting toward the plate I, which limits the rotation of the lever 39 in one direction around the pivot 31 by contacting against the inner surface of plate I, thus maintaining the outer projecting end 43 of the lever 39 spaced from the plate I.

Adjacent the outer end 43 of the lever 39, there may be mounted on the back plate 2, a second additional electromagnetic coil 44, provided with a compression helical spring 45 axial with a magnetic core 46 of the electromagnet which normally projects a stem 41 of the core 46 outside of the coil 44 into the space between the plates I and 2, as shown in Fig. 6. On the outer end of this stem 41, may be mounted a disk or plate 46, which may be spaced from the inside of the front plate I by means of a cushion 49. The leg 42 on the lever 39 thus spaces the end 43 sufficiently away from the inner face of the plate I, so that when the peg 33 on the wheel 24 pushes the lever longitudinally away from its pivot 31, the outer end 43 of the lever 39 will be projected into the axial path of the motion of the plate 49 connected to the electromagnetic core 46.

Thus, during automatic correction intervals, after the secondary clocks are speeded-up and their pegs 33 have pushed their levers 39 to their stop positions (that is, pushed their ends 43 into the axial paths of the plates 49 and maintained them there by the drive from motors 4 through the slippage of clutches 9") the stop release electromagnetic coils 44 are simultaneously energized to move their plates 48 to contact ends 43 and rock the levers 39 around their pivots 31 against the action of springs 4|, so that the projecting arms 49 will be moved beyond or over the heads of the pegs 33 on the gears 24 releasing said gears 24. The springs 4| will then retract the levers 39 again into the position shown in Fig. 6, but the pegs 33 will now be on the opposite sides of the stop arms 49, and the motors of the secondary clocks may continue to operate their clock hands 26 and 32 normally without obstruction until gears 24 with pegs 33 again contact the stop arms 49 upon the next revolution.

3. The master. clock control switch Referring now to Fig. 8, there is also employed in the master clock a similar lever mechanism 39 as described above and mounted in the same way, but instead of this lever carrying a definite stop arm 49 it is provided with a cam faced projection 59 so that the peg 33 on the minute hand wheel .24 will push the lever longitudinally so as to close a pair of contacts 5| and 52, one of which may be mounted on the lever 39. The time for this closure may be very short since the cammed projection 59 permits the peg 33 to move on without delay or retardation of the master clock, and to slide off the projection 59, opening again the contacts 5| and 52 by retraction of the lever 39 under the action of its spring 4|. It is these contacts 5| and 52 which start the automatic correction circuit for automatically speeding-up and releasing all the secondary clocks at exactly the same instant each hour according to the circuits shown in Fig. 1. This control circuit is made responsive even to the slightest closing of the contacts 5| and 52, and maintains itself operated during the entire correction interval, which, say for example, may be about one minute in duration as mentioned above. Since the lever 39 in the interval, stopped by arm 49, and released at the end of the correction interval;

(2) That a secondary clock was too fast and would be stopped by the lever arm 49 until it could be released at the exact moment by the completion of the correction interval set up by the master clock; and

(3) That a secondary clock was too slow and would be speeded-up during the correction interval for a time indication more than said interval and then stopped for release exactly at the proper instant and in correct time register with the master clock.

II. THE CONTROL CIRCUIT 1. Normal operation Referring to Fig. l the power supply may be normal volts 60 cycle alternating current which may be introduced into the circuit through the conductors 69 and circuit breakers or fuses 6| and a manual cut-off switch 62, located at the bottom central'portion of the circuit in Fig. 1. Let us assume that the manual switch 62 is closed and all of the clocks, both master and secondary clocks, are in their normal operation.

Current is supplied to the primary winding 63 of a transformer 64 which may be provided with two separate secondary windings, one secondary winding 65 for the alternating current supply for the synchronous induction motors of the clocks, and the other secondary winding 66 which may be provided with a central tap which is connected to a full wave rectifier 19 from which two different voltages of direct current may be withdrawn depending upon which pair of taps to the secondary coil 66 are connected across the alternating current input terminals of the rectifier 19.

Since one of the features of this invention is completely to control the secondary clocks over three conductors or wires, one of the electromagnetic coils provided in the secondary clocks, namely the release coils 44, are connected in series with the field windings 15 of the corresponding synchronous motors 4, so that in order to prevent too much energy being used up in the coils 44 the secondary winding 65 of the transformer may slightly step-up the alternating current voltage,

say from for example about 110 to volts, so

that these clocks will not be unnecessarily slowed down by the impedance of the coils 44 in series with the field windings 15. Similarly, in the master clock motor, which is operated from the same secondary windings 65, may have its field Winding 16 connected in series with an additional balancing coil 71, which corresponds in impedance to the coils 44, but does not operate an electromagnet or a release coil, in that such is not provided or necessary in the master clock circuit.

The conductors which are shown in heavy lines in Fig. 1 are common for all three of the currents employed in this control system.

The master clock motor 4 is energized by secondary Winding 65 through heavy conductors 89,

8i and 82 through balancing coil 11, field coil 16 and return conductors 83 and 84 to the secondary winding 65.

The secondary clock motors, however, are energized through a contact of an alternating current relay in the upper right hand corner of the circuit which is normally energized as long as the switch 62 is closed and the automatic correction circuit is not in operation. This relay 90 is energized from the secondary winding 65 through conductors 80, 8|, 9| to the negative terminal 92 of the rectifier 10, and then conductors 93 and 94 to normally closed cam operated contacts 95, conductor 96 through the coil of relay 90' and then back to the secondary winding 65 through conductors 91, 98, 99 and 84.

The motors 4 of the secondary clocks then have their field windings 15 energized also from the secondary winding 65 of transformer 64 through now closed contacts I of therelay 90 according to the following circuit: secondary winding 65, conductors 80 and MI, common conductor I02 for all of the secondary clocks, coils 44, windings 15, and back through the conductors I03 to common conductor I04, and thence conductor I05 which may pass through a fuse I06, conductors I01 and I08, closed contacts I00 of relay 90, conductors I09, H0, 98, 99 and 84 to the other terminal of the secondary winding 65.

The above traced circuits are those energized for the normal operation of all of the clocks outside of thecorrection intervals, with all of the secondary clocks separately operated by individual motors over a common alternating current supply circuit which also maintains the relay 90 energized.

2. Initiation of the correction control circuit As soon as the master clock has rotated its minute gear or wheel 24 through the normal clock mechanism, indicated in Fig. 1 as box III and containing the gear trains and clutches shown in Figs. 2, 3 and 4, so that the peg" 33 will. operate the lever 39 to close contacts 5| and 52', another alternating current circuit is closed to energize alternating current relay I20, which is the second relay from the left in the top row of alternating current relays shown in Fig. l. The circuit for the energization of this relay I20 is also taken from the alternating current supply of secondary winding '65 of transformer 64, which may be traced through conductors 80, BI, 9|, 93,'I2I, I22, I23, I24, normally closed cam operated contacts I25, conductor I26 to the coil of relay I20, and thence through conductor I21 to the master clock, now closed contacts 5I' and 52, conductor I28, from the master clock through conductors 83 and 84 to the other terminal of the secondary winding 65.

The energlzation of relay I20 closes its selfholding contacts I30 which bypass the contacts 5I and 52 in the master clock to maintain the relay I20 energized through the following ci'rcuit: secondary winding 65, conductors-80, BI, 9|, 93, I2I,, I22, I23, I24, cam operated contacts I25, conductor I26, relay I20, conductor I-3I, now closed self-holding contacts I30, conductors I32, I33, I34, H0, 96, 99 and 84 to the other terminal secondary winding 65. Thus, if the contacts 5I and 52 are only instantaneously closed the operation of relay I20 will be insuredfor the proper time in the correction cycle interval whencam I35 rotates. to open its contacts I25 breaking the above circuit to relay I20.

Relay I20" also closes" contacts I36 whi'ch energizes" the cam operating motor I which niay'r'o tate cam shaft I4I through a reduction gear or transmission mechanism I42, so that during the correction interval, shaft MI and the cams thereon make one complete rotation under the control of cam operated contacts I43, operated by the first cam I mounted on shaft MI. The circuit for the energization of the cam alternating current motor I40, which also may be an induction motor as motors 4 or any other type of motor without departing from the scope of this invention, is energized from the secondary winding 65 of the transformer 64 through conductors 80. 8|, 9|, 93, I2I, I22, I23, I46, I41, cam motor I40, conductors I48, I50, I5I, now closed contacts I36, conductors I52, I32, I33, I34, H0, 98, 99 and 84 tothe other terminal of secondary winding 65.

The closure of contacts I35 of relay I20 also energizes the relay I opening its contacts I56 and I51 to break the circuit for the manual advancing of all of the clock motors through the closure of manual switch I as will be described later in section 5 of this chapter II, so that if switch I60 is closed, its circuit will be opened so that the automatic correction under the control of the master clock through contacts 5I and 52 will not be effected by the manual operation of the switch I60.

7 The first contacts which are closed by the rotation of the cam shaft I4I after the encrgization 0f the cam motor I40 are contacts I43, which bypass the contacts I36 of the relay I20 and hold the motor I40 energized'until the cam follower on the contact I43 rides off the surface of the cam I45 again into the position shown in Fig. 1 after one revolution of cam shaft I4I. This holding circuit for the motor I40 may then be traced from the secondary winding through conductors 80, 8|, 9I,93, I2l, I22, I23, I46, I41, cam motor I40, conductors I48 and I6I, now closed cam operated contact I43, conductors I62, 99, and 84 to the other terminal of the secondary winding 65.

3. Speed-up secondary clocks Next relay to be operated is relay I10 whichv is energized by cam I10 closing of cam operated contacts I1I shortly after the closure of the contacts I43. The circuit for the energization of this relay is thus also from the secondary winding 65throughconductors 80, 8|, 9|, 93, I2I, I22, I12, just closed cam operated contacts I1 I, conductor I13, coil of relay I10, conductors I14, I33, I34, H0, 98,, 99 and 84 to the other terminal of the secondary windin 65.

The energization of relay I10 closes its con tacts I15 tov apply a low alternating current voltage from the other secondary winding 66 taken from the middle tap I16 of that winding, to the alternating current terminals of the rectifier 10 which thus produces the first and lower direct current voltage. This circuit through the recti'fier 10 is from the middle tap I16 through conductors I11, I18, now closed contacts I15, conductors I19 and I to one alternating current terminal I8I of rectifier 10, through the rectifier to the other alternating current terminal I82 and then conductor I83 which also may pass through a suitable fuse I84, and then conductor I85 to one end terminal of the secondary winding 66.

Now since the lower alternating current voltage is applied across terminals I8I and I82 of the rectifier 10, the lower of the two direct current voltages are applied; across the two other poles,

negative pole 92, positive pole I92, of the rectifier '10 completing a circuit energizing the speed-up coils I6 in all of the secondary clocks. The circuit from -'D. C. pole 92 through these coils I6 to +D. C. pole I92 may be traced as follows: conductors 9|, 8|, IOI, common conductor I02, through and back through common conductor I93, conductor I94 which may pass through a fuse I95, conductor I96, through the normally and now closed contact I91 of relay 90, conductors I98, I99 and 200 to the +D. C. pole I92. The simultaneous energization of all of the electromagnetic coils I6 in each of the secondary clocks of this system causes the retraction of their cores I (see Fig. 4) to engage the two crown-toothed clutch parts I4 and I9 so that the driving motors 4 still operating for each of the secondary clocks will speed-up the movement of the minute hands of each of the clocks for a period of, for example about 40 seconds of the one minute automatic correction interval, which is more than sufilcient for the pegs 33 on the wheels 24 to engage the stops 40 and push their levers 39 to their extreme end positions with their outer ends 43 projecting in the paths of the release magnet disks 48 (see Fig. 6). As soon as the levers 39 have been slid as far as possible to the ends of slots 33, their wheels 24 and minute and hour hands 28 and 32 will stop, and the clutches 9" will slip until the stop 40 are removed from the pegs 33 by the energization of the release magnets 44 described in the next chapter, or their motors 4 are deenergized.

After the cam shaft I4I has rotated for about of its complete revolution or namely for about 40 seconds, cam I opens the contact I1I again breaking the circuit through relay I10 so that this relay becomes deenergized and breaks the lower potential alternating current circuit applied across contacts I8I and I82 of the rectifier 10, which therefore cuts off the energy for the lower D. C. circuit deenergizingthe electromagnetic coils I6 in each of the secondary clocks, so

that the clock motors are now operated again at a regular speed although their hands are still stopped by levers 39.

4. Stop release of secondary clocks Shortly after the opening of the contact I1I by cam I10, another cam 20I opens the contacts 95 breaking the circuit to the relay 90 which then deenergizes, opening the circuit between contacts I00 and I91 and closing contacts 292. The opening of contacts I00 breaks the alternating current circuit to the motors 4 of each of the secondary clocks, so that these motors are now stopped during the remaining few seconds (about 4 seconds which is suificient for motors to come to rest) of the correction interval, so that the higher direct current voltage may be applied over the same circuit to energize the stop release coils 44 connected in series with the field windings of the synchronous induction motors 4. The

opening of contacts I91 directly breaks the lower D. C. circuit through coils I6 in the secondary clocks, so that the motors 4 remain geared again at their regular speeds by the engagement of gear I2 (see Fig. 3) with friction disk to pinion 2I under the action of spring I8. The making of the contacts 202 connects the higher D. C. circuit across terminals 92 and I92 of rectifier 10 with the stop release magnet coils 44 in series with the field coils 15 in each of the secondary clocks p p ato y to the ap icat cn .of .a hi h each of the electromagnetic coils I6,

10 alternating current across the A. C. terminals I8I and I82 of the rectifier 10.

Immediately thereafter, further rotation of the cam shaft I4I, causes cam 205 to close its cam operated contacts 206 to energize the higher voltage alternating current circuit, by first energization of relay 2I0 through the circuit of the secondary winding 65, conductors 80, 8I, 9|, 93, I2I, 2II, just closed cam operated contact 206, conductor 2I2 to the coil of relay 2I0, and thence through conductors 2I3, I34, H0, 98, 99 and 84 to the other terminal of the secondary winding 65. The energization of relay 2I0 closes contacts 2I5 which closes the higher voltage A. C. circuit through the other secondary winding 66 of the transformer 64 as follows: one end of the coil 66 through conductor 2I6 now closed contacts 2I5 of relay 2I0, conductors I19, I80, to the A. C. terminal I 8| of rectifier 10, through the rectifier 10 and then from A. C. terminal I82 through conductor I83, fuse I84, and conductor I85 to the other end of the secondary winding 66.

The opening of contacts 2I1 by the energization of relay 2 I0 breaks the circuit again through the manual switch I60 mentioned above, so that in the next sequence when relay I20 and I55 will be deenergized before the completion of the correction interval, operation of the switch I60 will have no effect on the automatic correction cycle.

The application of the higher A. C. voltage across terminals I8I and I82 of rectifier 10 now supplies a higher D. C. voltage in the circuit from D. C. pole 92, through conductors 9|, BI, IOI, common conductor I02, stop release coils 44 and held windings 15 and conductor I03 of each of the secondary clocks, and thence through common conductor I04, conductor I05, fuse I06, and

conductor I01, already closed contacts 202 of deenergized relay 90, conductors 2 I8, I99 and 200 to the +D. C. pole I92 of the rectifier 10. With this higher D. C. voltage now applied in series through winding 15, electromagnetic coils 44 are sufficiently and simultaneously energized to retract their cores 46 (see Fig. 6) together with their extensions 41 so that the disks 48 will contact the ends 43 of the extended stop levers 39 to move the stop arms 40 over the ends of pegs 33 for the springs M to retract these levers 39 back into their normal positions shown in Fig. 6, with the pegs 33 released and ready to continue the operation of the clocks as soon as the motors 4 for the secondary clocks are again started.

The energization of release coils 44 continues until the cam 205 rotates to open contacts 206 again breaking the circuit to relay 2| 0, which removes the higher A. C. voltage from A. C. terminals I8I and I82 of the rectifier 10, and correspondingly cuts-off the high D. C. voltage supply to the circuit through release coils 44 in each of the secondary clock circuits.

Right after and during the closure of the cam contacts 206, cam I35 opens its cam operated contact I25 which deenergizes the circuit to relay I20 causing this relay to release, which in turn breaks the circuit to relay I55 by the opening of contact I36, causing relay I55 to release so that relays I20 and I55 are again in the position shown in Fig. 1 preparatory to normal operation of the secondary clocks.

Then after the cam contacts 206 are opened and release coils 44 deenergized, the cam 20I closes again contacts 95 for energizing again the relay 90, which according to the above traced circuits in section 1 above of this chapter II, again starts the secondary motors 4 for all the secondary clocks and the circuit is accordingly in normal operation again. Since the restarting of all the secondary clock motors is simultaneous and instantaneous, they are accordingly all in proper register with each other and the master clock.

Synchronized closely with the re-closure of the contacts 95 by the operation of cam 29I, the first cam I45 opens the contacts I43 in the circuit to the cam motor I49, so that this cam motor now will stop in the position shown in Fig. 1, indicat ing the end of the correction interval and the starting position for the next automatic correction interval.

5. Manual reset circuit If it is desired to correct the time of the master clock by advancing it, and simultaneously there.- with advancing of all of the secondary clocks, so that all the clocks of the system will be in register with each other, the manual switch I69 near the upper left hand corner of the circuit of Fig. 1 may be closed to accomplish this result, at any time except during an automatic correction interval.

The closure of this double pole manual switch I90, completes the lower A. C. circuit to A. C. terminals I8! and I82 of the rectifier In from the center tap I'IB of the other secondary winding 69 of transformer I54, through conductors I'I'i, 220, contact 22I of switch I50, now and normally closed contacts I56 of deenergized relay I55, conductor 222, now and normally closed contacts 2 I? of deenergized relay 2 I9, conductors 223, and I80, to terminal I8I, through the rectifier Ti), and thence from the other A. C. terminal I82 through conductor I83, fuse I84 and conductor I85 to an end terminal of said other secondary coil 96. The low A. C. voltage now applied to the rectifier 10 supplies a lower voltage D. C. circuit which may be traced through each of the speed-up coils I9 not only in the secondary clocks but also through speed-up coil I6 in the master clock, which corresponds physically with electromagnetic coils I6 previously described in Figs. 2, 3 and 4, as follows: from -D. C. pole 92 of rectifiers 10, through conductors 9|, 8|, IIII, I02, coils It of each of the secondary clocks, conductors I93, I94, fuse I95, conductor I95, now closed contacts I91 of relay 9!], conductors I98, I99 and 200 to the +D. C. pole I92; and simultaneously parallel to this circuit a similar D. C. circuit from D. C. pole 92, through conductors 9i, 82, speedup coil I6 of the master clock, conductor 225, now closed contacts I! of relay I55, contact 224 of switch I60, and then conductors 22B and 200 to the +D. C. pole I92 of the rectifier 10. Thus, as long as the manual switch 60 is maintained manually closed all of the clocks, both master and secondary, will be speeded up at a rate of about 60 times their normal speed until all the clocks are at the desired indicated time, at which time the switch I60 must be manually opened or released. It should be noted, however, that this speed of advance cannot be made for more than 59 minutes at a time, because as soon as the pegs 33 in each of the clocks, including the master clock, engage their corresponding stop arms 49 and cam arm 50, respectively, this manual advancing circuit will be automatically cut-out according to the operation described above in sections 2, 3 and 4 of this chapter II. Thus, for resetting the clock for each hour of delay, it will take 2 minutes of time for the closure for the manual switch I60, one minute for the 59 minutes advance at fast rate, and another minutetor the 60th minute of each hour in which the automatic correction interval occurs, after which interval the clocks will again advance fast for the next 59 minutes if manual switch IE9 is still closed, and so on until the manual switch IE0 is opened.

Advantageous features of the present invention include separate relays for each of the cam operated switches, and these cam operated switches only operate their corresponding relays with the actual current for operating the motors and coils in the clocks of the system connected through the contacts of these relays, thus enabling much higher currents to be controlled than could be controlled through cam operated switches, such as currents for a system of a large number of secondary clocks. Another advantage is in the construction, of the pivoted and slidable lever 39 and released mechanism for the stopping device in the secondary motors, which are definite and positive in their action. Still another advantage is that both of the electromagnetic coils in the secondary clocks, are connected in separate control circuits and not necessarily required to rely upon potential level selection for operation, All ofthe relays of the control circuit are alternating current relays and operated by the v. or v. alternating current supply, and all of the electromagnetic control coils I6, I6 and 44 are operated only by direct current. Another feature of the present invention is the employment of the additional friction clutch 9 at the input driving connection to prevent both (1) the stalling of any of the motors when stopped at their output regardless of the speed of drive of the output, and to prevent (2) the winding up of the gears in the clocks between their inputs and outputs, such as by taking up the back lash in the gears and then placing torsion in the shafts between pairs of gears on the same shaft, by the continued torque from the motor when the clocks are stopped near their outputs while their motors are still energized, so that when the stops are released the hands at the outputs of the clocks will not jump ahead and give an incorrect time indication.

While there is described above the principles of this invention in connection with specific apparatus, it is to beclearl'y understood that this description is made only by way of example and not as a limitation to the scope of this invention.

What is claimed is:

1. In a system for synchronizing at predetermined intervals a secondary electric clock with a master clock said secondary clock having a time disclosing movement, said secondary clock being operated by an alternating current synchronous motor having a field winding, said system comprising: analternating current source, two direct current sources of different voltage, and three conductors connecting said clocks and sources, one pair of said three conductors conducting selectively the alternating current from said source for said motors and one voltage of said direct currents, another pair of said three conductors conducting the other voltage of said direct currents, means in said secondary clock to stop its time-disclosing movement, means controlled by one of said direct currents adapted to speed up the movement of said secondary clock, and means controlled by the other of said direct currents for releasing said stop means including an electromagnetic coil in series with said field winding of each of said secondary clock motors, and means in said master clock for controlling said direct current controlled means at said predetermined intervals.

2. A system according to claim 1 wherein said two direct current sources include a transformer connected to said alternating current source, a rectifier connected to said transformer and separate taps from said transformer to said rectifier.

3. A system according to claim 1 wherein said stop means includes a projection on a rotating means, a slidable lever and a projection engaging arm mounted on said lever for moving said lever in one direction.

4. A system according to claim 3 wherein said stop release means also includes a plunger controlled by said electromagnetic coil, and a lever engaging means mounted on said plunger for disengaging said arm from said projection by movement of said lever in a direction at right angles to the movement imparted to said lever by said projection.

5. A system according to claim 4 including a spring connected to said lever for restoring said lever whereby said arm is again in a projection engaging position after the operation of said stop release means.

6. A system according to claim 1 including manual means for speeding-up both said secondary and said master clocks simultaneously.

7. A system according to claim 6 including interlocking means to prevent said speeding-up by said manual means during said predetermined intervals.

8. In a system for synchronizing secondary electric clocks with a master electric clock, said secondary clocks each having a time-disclosing movement and being operated by a synchronous electric motor, the improvement comprising:

14 means in each secondary clock for setting said secondary clock under the control of the master clock at predetermined intervals, a pair of current supply conductors connecting the motor of each secondary clock in parallel, each secondary clock motor having a field winding, said setting means comprising a clutch adapted for speeding up the movement of each said secondary clock, a first electromagnetic coil in each secondary clock for operating said clutch, a stop device for stopping the movement of the hands of each secondary clock, a second electromagnetic coil in each said secondary clock for releasing said stop device, control means in said master clock for.

consecutively operating said first and said second electromagnetic coils, a third conductor connected to each of said first electromagnetic coils in each of said secondary clocks, each of said second electromagnetic coils being connected in series with its associated field winding, one of said pair of conductors being connected to both of said coils in each secondary clock, whereby the motors of said secondary clocks and their coils are energized separately over only three conductors.

LEWIS J. STERN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,310,787 Bryce July 22, 1919 1,377,000 Bryce May 3, 1921 1,930,256 Sprecker Oct. 10, 1933 2,120,353 Faller June 14, 1938 2,167,829 Faller Aug. 1, 1939 2,498,462 Stern Feb. 21, 1950 

